This invention relates to a metallic catalyst, particularly to a metallic catalyst applicable to recombination of oxygen and hydrogen present in a reactor off-gas to water, and also to a process for preparing said metallic catalyst.
Heretofore, various kinds of catalysts have been employed in many fields including the chemical industry and the atomic power generation to remove impurities from effluent gases and product gases or produce the desired products. A low cost, a high catalytic performance, that is, a high catalytic activity, and a high mechanical strength are required for these catalysts, and catalysts have been researched and developed to satisfy these requirements. However, the performance of a catalyst depends mainly upon a catalyst metal. Thus, in order to improve the catalytic activity, it is necessary to increase a surface area of a catalyst carrier and uniformly distribute the catalytic metal on the carrier. To this end, ceramics such as alumina, etc. have been so far employed as a catalyst carrier, and catalyst metal is supported on the carrier. That is, the so-called ceramic catalysts have been used. However, this type of the catalysts are readily susceptible to attrition owing to vibrations generated when packed or while used, and the resulting catalyst powder scatters, often causing a local reaction or troubles such as cloggings, etc. to apparatuses, devices, etc. such as valves. Furthermore, the performance of the catalyst itself, that is, catalytic activity, is deteriorated by the attrition.
As a substitute, a metallic catalyst consisting of a metal having a high attrition resistance as a carrier, and a catalyst metal supported thereon has been proposed, and employed. Though the metallic catalyst is hardly susceptible to the attrition owing to the vibration when packed, etc., a catalyst performance is generally low, and the thickness of a catalyst layer is large.
To improve these disadvantages of such a metallic catalyst, other metallic catalysts have been proposed (U.S. Pat. Nos. 3,712,856 and 3,956,189). However, in the proposed metallic catalysts, catalyst metal palladium is mainly supported on alumina locally exposed to the surface of catalyst carrier, and thus the entire surface of the catalyst carrier is not utilized, and an improvement of the catalytic activity cannot be expected so much. Furthermore, a portion of the catalyst metal palladium is in direct contact with the metallic carrier, and thus a temperature drop of the catalyst metal is so large that, in a low temperature gas atmosphere, the heat of reaction cannot be retained on the catalyst metal, lowering the catalytic activity.